The present invention relates to semiconductor structures, and more particularly to semiconductor structures including an image sensor pixel employing a shared floating diffusion, methods of operating the same, and a design structure for the same.
An image sensor converts a visual image to digital data that may be represented as a picture. The image sensor includes an array of pixels, which are unit devices for the conversion of the visual image into digital data. Digital cameras and optical imaging devices employ an image sensor. Image sensors include charge-coupled devices (CCDs) or complementary metal oxide semiconductor (CMOS) sensors.
While CMOS image sensors have been more recently developed compared to CCDs, CMOS image sensors provide an advantage of lower power consumption, smaller size, and faster data processing than CCDs as well as direct digital output that is not available in CCDs. Also, CMOS image sensors have lower manufacturing cost compared with CCDs since many standard semiconductor manufacturing processes may be employed to manufacture CMOS image sensors. For these reasons, commercial employment of CMOS image sensors has been steadily increasing in recent years.
A key performance metric of a pixel of an image sensor is the level of the leakage current from photodiodes to the electrical ground in the substrate or to an adjacent semiconductor device. Such leakage current is known to be proportional to the length of the perimeter of a photodiode, i.e., the length of the interface between the photodiode and shallow trench isolation structures.
Another key performance metric of the pixel of the image sensor is the density of semiconductor devices on the surface of the substrate. Particularly, designs that employ dummy devices that occupy an area for the purpose of maintaining a uniform pattern factor during semiconductor processing does not fully utilize all available areas of the semiconductor substrate.
Yet another key performance metric of the pixel of the image sensor is the density of metal wiring, and particularly the first level metal wiring that is closest to the photodiodes, that blocks light that impinges onto the photodiodes. In general, the lesser the area occupied by metal wiring, the more the transmission of light from the top surface of dielectric layers above the semiconductor substrate to the photodiodes, and consequently, the greater the efficiency of the photodiodes.